The controlling apparatus for an industrial product of this disclosure has a couple of microcomputers each of which has a CPU and a memory and each of which runs the same controlling program as well as the same diagnostic program sequence parallelly and simultaneously. After the CPU of the microcomputer writes the calculated result of the diagnostic program sequence in the predetermined area of the storing area for monitoring value, such CPU send the same calculated result to the other one of the microcomputers (receiving microcomputer). The CPU of the receiving microcomputer makes a diagnosis for finding whether or not the received result is identical with its own calculated result.